SMB signing has been present on the Windows server platform since WinNT but hasn't been defaulted to ON until Win2003 Server was released. I've been having the exact same issue at my school ever since they updated from Win2k to Win2k3. The admin is a great guy but refuses to budge on turning SMB singing off even though it has rendered all Mac users unable to use the network. So much for a heterogenious environment...

I've tried using the built-in Samba on OS X in addition to Thursby's Dave and ADmitMac products. Nothing has worked and Thursby is definately aware of the issue based upon this statement in their FAQ section :

Quote:

Question: Does DAVE or ADmitMac work with Windows Server 2003?

Answer: In order for the current version of ADmitMac or DAVE to work with Windows Server 2003, you must disable SMB signings and make sure that the authentication method is not set to NTLMv2 only. Currently, neither DAVE nor ADmitMac supports either option.

Anyway, supposedly SMB singing is a new feature in the recently released Samba 3.0 which is still in beta but I've been unable to compile it for OS X successfully...Mainly because I don't know what I'm doing. Any help would be appreciated.